[Skiboot] [RFC PATCH v3 4/6] xscoms: read/write xscoms using ucall

[Ryan Grimm]

From: Madhavan Srinivasan <maddy at linux.vnet.ibm.com>

xscom registers are in the secure memory area when secure mode is
enabled. These registers cannot be accessed directly and need to use
ultravisor services using ultracall.

Signed-off-by: Madhavan Srinivasan <maddy at linux.vnet.ibm.com>
Signed-off-by: Santosh Sivaraj <santosh at fossix.org>
[ linuxram: Set uv_present just after starting UV ]
Signed-off-by: Ram Pai <linuxram at us.ibm.com>
[ grimm: Don't check MSR in xscom read/write ]
Signed-off-by: Ryan Grimm <grimm at linux.ibm.com>
---
 hw/ultravisor.c      |  4 ++++
 include/ultravisor.h | 22 ++++++++++++++++++++++
 include/xscom.h      | 11 +++++++++--
 3 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/hw/ultravisor.c b/hw/ultravisor.c
index d55d752b..a5553757 100644
--- a/hw/ultravisor.c
+++ b/hw/ultravisor.c
@@ -17,6 +17,7 @@
 #include <libfdt/libfdt.h>
 #include <libstb/container.h>
 
+bool uv_present = false;
 static char *uv_image = NULL;
 static size_t uv_image_size;
 struct xz_decompress *uv_xz = NULL;
@@ -251,6 +252,9 @@ int start_ultravisor(void)
 
 	cpu_start_ultravisor((void *)uv_opal);
 
+	/* From now on XSCOM must go through ucall */
+	uv_present = true;
+
 	while (i > 0)
 		cpu_wait_job(jobs[--i], true);
 
diff --git a/include/ultravisor.h b/include/ultravisor.h
index daeb99b6..d212f463 100644
--- a/include/ultravisor.h
+++ b/include/ultravisor.h
@@ -12,10 +12,15 @@
  * for the secure virtual machines */
 #define UV_SECURE_MEM_BIT              (PPC_BIT(15))
 #define MAX_COMPRESSED_UV_IMAGE_SIZE 0x40000 /* 256 Kilobytes */
+#define UV_READ_SCOM  0xF114
+#define UV_WRITE_SCOM 0xF118
+#define UCALL_BUFSIZE 4
 #define UV_ACCESS_BIT		0x1ULL << 48
 #define UV_LOAD_MAX_SIZE	0x200000
 #define UV_FDT_MAX_SIZE		0x100000
 
+extern bool uv_present;
+
 extern int start_uv(uint64_t entry, struct uv_opal *uv_opal);
 extern bool uv_add_mem_range(__be64 start, __be64 end);
 extern void uv_preload_image(void);
@@ -24,4 +29,21 @@ extern void init_uv(void);
 extern int start_ultravisor(void);
 extern long ucall(unsigned long opcode, unsigned long *retbuf, ...);
 
+static inline int uv_xscom_read(u64 partid, u64 pcb_addr, u64 *val)
+{
+	long rc;
+	unsigned long retbuf[UCALL_BUFSIZE];
+
+	rc = ucall(UV_READ_SCOM, retbuf, partid, pcb_addr);
+	*val = retbuf[0];
+	return rc;
+}
+
+static inline int uv_xscom_write(u64 partid, u64 pcb_addr, u64 val)
+{
+	unsigned long retbuf[UCALL_BUFSIZE];
+
+	return ucall(UV_WRITE_SCOM, retbuf, partid, pcb_addr, val);
+}
+
 #endif /* __ULTRAVISOR_H */
diff --git a/include/xscom.h b/include/xscom.h
index 8a466d56..2f4c819b 100644
--- a/include/xscom.h
+++ b/include/xscom.h
@@ -7,6 +7,7 @@
 #include <stdint.h>
 #include <processor.h>
 #include <cpu.h>
+#include <ultravisor.h>
 
 /*
  * SCOM "partID" definitions:
@@ -174,10 +175,16 @@ extern void _xscom_unlock(void);
 /* Targeted SCOM access */
 static inline int xscom_read(uint32_t partid, uint64_t pcb_addr, uint64_t *val)
 {
-	return _xscom_read(partid, pcb_addr, val, true);
+	if (!uv_present)
+		return _xscom_read(partid, pcb_addr, val, true);
+
+	return uv_xscom_read(partid, pcb_addr, val);
 }
 static inline int xscom_write(uint32_t partid, uint64_t pcb_addr, uint64_t val) {
-	return _xscom_write(partid, pcb_addr, val, true);
+	if (!uv_present)
+		return _xscom_write(partid, pcb_addr, val, true);
+
+	return uv_xscom_write(partid, pcb_addr, val);
 }
 extern int xscom_write_mask(uint32_t partid, uint64_t pcb_addr, uint64_t val, uint64_t mask);
 
-- 
2.21.0